The current design of vertical axis wind turbines (VAWTs) suffers from inevitable change in tip speed ratio, λ, in variant wind conditions due to fixed rotor speed. At relatively high wind speeds, ...which are promising due to high wind power potential, VAWTs operate at low λ with poor power coefficient. Morphing airfoils can be a potential solution by modifying the airfoil shape to optimal at each λ. The optimal airfoil shape for VAWTs at low λ, where dynamic stall is present, has not yet been studied in the literature, therefore, the present study addresses this gap by focusing on this regime to serve as a step towards designing morphing airfoils for VAWTs by identifying the optimal airfoil shape at low λ. The present study performs a combined analysis of three shape defining parameters, namely the airfoil maximum thickness and its position as well as the leading-edge radius, to reveal the overall design space. The analysis is based on 252 high-fidelity transient CFD simulations of 126 identical airfoil shapes. The simulations are verified and validated with three experiments. The results show that the three shape defining parameters have a fully coupled impact on the turbine power and thrust coefficients. When λ reduces from 3.0 to 2.5, the optimal airfoil changes from NACA0018–4.5/2.75 to NACA0024–4.5/3.5, that is increasing the maximum thickness from 18%c to 24%c and shifting its position from 27.5%c to 35%c, while the leading-edge radius index, I, remains 4.5. In general, reducing I from the default value of 6.0 to 4.5 is found to increase the turbine CP.
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The automated design of synchronous reluctance (SyR) motors based on multiobjective genetic optimization and finite-element analysis is considered in this paper. Three types of barrier shapes are ...considered, all described by an effective limited set of input variables. The three solutions are investigated to establish which of the geometries can give the best torque output and also which one represents the best compromise between output performance and computational time. The analysis presented in this paper shows that SyR motors designed automatically can give a good performance and can be designed in a reasonable time, and it is also shown that not all design degrees of freedom are useful in terms of motor performance. Two prototypes of automatically designed machines have been fabricated and experimentally compared with a third prototype designed according to state-of-the-art design principles.
The performance-enhancing effects of closely packing tidal turbines in single row arrays (tidal fences) are evaluated in this computational study. Infinitely long tidal fences are simulated with a ...range of lateral rotor spacings using a blade element momentum method embedded in a Reynolds averaged Navier–Stokes solver (RANS-BEM).
First, a rotor design tool is applied to determine a hydrodynamically optimal rotor design for each lateral spacing. In the RANS-BEM method, the effect of blockage (the ratio of rotor swept area to channel cross-sectional area) on rotor optimization is accounted for. Increased blockage is found to result in increased optimal solidity and decreased optimal pitch. Next, each rotor design is simulated in its design spacing as well as several off-design spacings. The resulting power coefficient is largest when the rotor optimized for the highest blockage case operates in the array with the closest lateral spacing. Further, although a rotor's performance is improved through operation at a blockage higher than its design point, it still exhibits inferior performance relative to a rotor designed for that higher blockage. The results indicate that blockage must be considered in the rotor design process if the optimal rotor efficiency for a given spacing is to be achieved.
•We design tidal turbine rotors for blocked flow conditions using a RANS-BEM model.•Designing rotors for operating blockage conditions improves the power coefficient.•Rotors designed for high blockage conditions require increased solidity.•Rotors designed for high blockage perform poorly in unblocked flow conditions.
The paper presents a study on the aerodynamic design of self-rectifying biradial turbine rotors for applications in wave energy conversion. The aim is to improve the biradial turbine efficiency and ...understand the specific speed range for which the turbine operation is most efficient. A rotor geometry generation method is presented, adding more degrees of freedom to the original method by improving the rotor meridional profile definition and relative flow velocity distribution. The new meridional channel definition allows tuning the rotor specific speed in the design phase. The prescribed relative flow velocity distribution improves the rotor inlet-to-outlet pressure gradient distribution. The research comprises geometry parametrisation, and three-dimensional flow simulations with a Reynolds-averaged Navier–Stokes equations solver to understand the effect of the design parameters on the rotor performance. The increase in total-to-total efficiency of the new rotor design is near 1%, demonstrating the good aerodynamic performance of the original design. It is shown that the turbine’s specific speed can increase by 5.4%, and the specific diameter can decrease by 6.0% compared to the original design without reducing turbine efficiency.
•An improved design method for biradial rotors is presented.•The impact of the design parameters over efficiency is studied.•New geometries with efficiency gains of 1% were obtained.•A high specific speed biradial rotor was designed.
This paper presents a method for multidisciplinary design optimization of offshore wind turbines at system level. The formulation and implementation that enable the integrated aerodynamic and ...structural design of the rotor and tower simultaneously are detailed. The objective function to be minimized is the levelized cost of energy. The model includes various design constraints: stresses, deflections, modal frequencies and fatigue limits along different stations of the blade and tower. The rotor design variables are: chord and twist distribution, blade length, rated rotational speed and structural thicknesses along the span. The tower design variables are: tower thickness and diameter distribution, as well as the tower height. For the other wind turbine components, a representative mass model is used to include their dynamic interactions in the system. To calculate the system costs, representative cost models of a wind turbine located in an offshore wind farm are used. To show the potential of the method and to verify its usefulness, the 5 MW NREL wind turbine is used as a case study. The result of the design optimization process shows 2.3% decrease in the levelized cost of energy for a representative Dutch site, while satisfying all the design constraints.
•A framework for wind turbine multidisciplinary design optimization is presented.•Rotor and tower are optimized simultaneously with multiple design constraints.•The properties of all the components are considered using mass and cost models.•The integrated framework reduced the levelized cost of energy by 2.3%.
Social and political concerns on climate change have made renewable energy an essential component of government’s work plans. Grid-connected horizontal-axis hydrokinetic turbines are promising ...eco-friendly power sources for electrical energy supply to households near middle-to-high discharge rivers, while providing an opportunity to sell the energy surplus. In this work, a rotor design analysis of a hydrokinetic turbine with a 1 m nominal radius is performed based on blade element momentum theory. Then, an economic analysis is presented in terms of the discounted payback period and the internal rate of return. The numerical results show that three-bladed hydrokinetic turbines with a nominal tip speed ratio of 5 and state-of-the art high lift-to-drag ratio hydrofoils (∼100) lead to maximum performance with a power coefficient around 0.45. Performance can be further improved in an affordable manner using diffuser-augmented hydrokinetic turbines. The use of hydrokinetic energy in household applications can be profitable in leading economic countries with a discounted payback period of 4–6 years. In energy developing countries, this technological solution can be cost effective accompanied by economic subsides and implementation of a local industry, resulting in similar payback periods.
•Hydrokinetic energy for household applications in middle-to-high discharge rivers is analyzed.•Rotor design using BEM theory and economic analysis are presented.•Three blades with a tip speed ratio of 5 and high Cl/Cd maximize performance.•The investment is profitable with a discounted payback period of 4–6 years.•Economic subsides in countries with a high discount rate are necessary.
A new sub-scale field-prototype design solution is developed to realize the dynamics, structural response, and distributed loads (gravitational, aerodynamic, centrifugal) that are characteristic of a ...full-scale large, modern wind turbine rotor. Prior work in sub-scale wind turbine testing has focused on matching aerodynamic/aero-elastic characteristics of full-scale rotors at wind tunnel scale. However, large-scale rotor designs must expand beyond this limited set of scaling parameters for cost-effective prototyping and meet strict requirements for structural safety for field testing. Here, the challenge lies in producing a structural design meeting two competing objectives: novel scaling objectives that prescribe the sub-scale blade to have low mass and stiffness; and traditional structural safety objectives that drive the design to have higher stiffness and mass. A 20% gravo-aeroelastically scaled wind turbine blade is developed successfully that satisfies these competing objectives. First, it achieved close agreement for non-dimensional tip deflection and flap-wise blade frequency (both within 2.1%) with a blade mass distribution constrained to produce target gravitational and centrifugal loads. Second, the entire blade structure was optimized to ensure a safe, manufacturable solution meeting strict strength requirements for a testing site that can experience up to 45 m/s wind gusts. The prototype-scale blade was fabricated and successfully proof-load tested.
Due to the significant advantages of cost savings, low temperature rises and high efficiency, synchronous reluctance machines (SynRMs) have attracted growing interest from academia to industrial ...applications. Numerous articles have been published to obtain a SynRM with improved performance (i.e., a high torque density and efficiency and a lower torque ripple) using different focusing points at healthy and faulty conditions such as rotor design, magnetic steel grade, stator winding, and fault tolerance control (FTC) strategy. Hence, this article reviews the scientific researches about SynRMs aiming to improve their performance. These scientific researches can be categorized into four sections: 1) optimal rotor design; 2) magnetic steel grade; 3) winding configurations; and 4) FTC strategies.
Surface permanent magnet synchronous machines are one of the most widely adopted machine topologies in high-speed applications where efficiency and power factor cannot be compromised. Although the ...design of such machine type has been extensively investigated in both industry and academia, this work aims at addressing its limitations when applied in high-speed applications. First, this paper proposes an accurate design methodology for continuous-duty high-speed surface-mounted permanent magnets synchronous machines, capable of accounting for the rise of the speed-dependent losses and structural needs with a limited impact on the computational burden. The outlined approach can be used to speed-up the initial design stage as it allows to reduce the number of solutions to evaluate before commencing the refinement stages required before the definition of the final design. Indeed, the introduced design approach is used to systematically assess the maximum power capability as function of the maximum speed and the airgap thickness for a given outer envelope and cooling system. The influence of the high-speed limiting factors is deeply investigated also considering their effects on the machine geometries providing the highest torque. The selection of the final design is discussed and justified. Experimental results of the 4.2 kW-80 kprm prototype validate the design methodology.
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